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How to remove chemicals from wastewater

Sir,

I am doing b.tech in chemicals(6th sem). Sir, I am doing my industrial training in a company deals in artificial limbs, etc. Sir, during electroplating I saw the waste from zinc plating, chrome plating and polishing are mixed and send to effluent plant where it is treated with lime , FeSO4, H2SO4 to control its pH values. My question is if we treat with all these chems, we just maintain its pH value neither than to remove the chemicals. please anwser my ques. I shall be highly thankful to u.

ANUJ SHARMA
- KANPUR, U.P, INDIA
2003

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It's a matter of local and national laws. But here in the USA, simply adjusting the pH is absolutely not sufficient. First, any necessary pretreatment must be done so that when the pH is adjusted the metals will precipitate; then the pH is adjusted and the metals drop out; then the metals must be "filtered" out of the wastewater. No metals (well, almost no amount) are allowed in the discharge either as solids nor as soluble compounds

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

The chemistry you have described is a general approach to metal removal providing you have a precipitation or settlement step on the plant rather than just ph correction and discharge. The FeSO4 is present as ferrous which under acid conditions will reduce the chrome from its insoluble 6+ state to the insoluble 3+ state when it is neutralised. The problem with precipitating mixed metals is that they all have an optimum pH at which they are most insoluble, this difference can be quite large.

Hamish McWillie
- Northamptonshire, UK
2003